Sealing composition and its use

ABSTRACT

A method for sealing rock or soil comprising inserting a sealing composition obtained by mixing a silica sol and at least one gelling agent, wherein the silica sol has an S-value higher than about 72%, a method for preparing the sealing composition and the composition obtained from the method.

This application is a division of U.S. application Ser. No. 10/272,165,filed Oct. 16, 2002, which claims priority from Provisional PatentApplication No. 60/330,445, filed Oct. 18, 2001.

The present invention relates to a method for sealing rock or soilcomprising inserting a sealing composition obtained by mixing a silicasol having an S-value higher than about 72% and at least one gellingagent into said rock or soil. The invention also relates to such acomposition and a method for preparing the composition.

BACKGROUND OF THE INVENTION

The requirements and performance of compositions used for sealing rockand soil have increased in the course of time. These requirementsinvolve both improved environmental and technical aspects. Previously,various plastics and polymers involving toxic substances have beenemployed to seal water leaks in e.g. concrete walls, tunnels, orcavities formed on the back side of a concrete wall. Such sealingchemicals have in a number of cases caused contamination of groundwaterand health problems to e.g. construction workers handling them. However,attempts have been made to replace hazardous products with moreenvironmentally adapted ones. New products have also been sought for tomeet the recently imposed leakage restrictions. In some instances, waterleakage levels below 1 liter/(min*100 meters) have been the upperthreshold on constructions sites of tunnels. This have forced thesuppliers to provide technically improved sealing products. U.S. Pat.No. 5,396,749 describes a method for cutting off water flow by groutingwhereby troubles due to water leakage and collapse of ground isprevented. The cut-off agent is prepared by mixing e.g. colloidalsilica, inorganic salt, and a water-soluble urethane polymer.

However, the strength of these agents has shown to be insufficient inseveral applications, particularly where the agent during injection andgelling is exposed to a high water pressure. Especially unstable agentshave during the ageing phase resulted in a fairly low long termstrength. Sealing agents have also been used for sealing soil to preventleakage of contaminants in subterranean areas like buried sources, wastedumps etc. U.S. Pat. No. 5,836,390 describes a method of formingsubsurface barriers where a viscous liquid comprising e.g. polybutenes,polysiloxanes, and colloidal silica is injected.

It is desirable to provide an environmentally adapted liquid cut-offagent having a high long term strength, especially in the field ofsealing rock, where the cut-off agents may be subjected to high waterpressure from groundwater. It is also desirable to provide durableproducts which resist washout forces and having a low permeability, i.e.impermeable to water and other liquids.

It is an object of the present invention to provide such productssolving the drawbacks of the prior art referred to above.

THE INVENTION

The present invention relates to a method for sealing rock or soilcomprising inserting a sealing composition obtained by mixing a silicasol having an S-value higher than about 72% and at least one gellingagent into said rock or soil.

Preferably, the sealing concerns cutting off a liquid flow in a leakingpart or cavity. The present invention also relates to a method forpreparing a sealing composition, which comprises mixing a silica solhaving an S-value higher than about 72% and at least one gelling agent.The present invention also relates to a sealing composition obtained bythis method.

It has been surprisingly found that a silica sol having a high S-value,i.e. an S-value higher than about 72%, can impart a high long term gelstrength to a sealing composition. The term “gel strength” as usedherein is a measure of the shear and compressive strength of the gelledsealing composition that develops with time. A high long term strengthprovides a durable sealing. It has also been found that the sealingcomposition according to the present invention has a low permeability,which indicates good sealing characteristics.

The “S-value” characterises the extent of aggregation of the silicaparticles in the silica sol, Le. the degree of aggregate or microgelformation. The S-value of the silica sol has been measured andcalculated according to the formulas given in ller, R K. & Dalton, R L.in J. Phys. Chem. 60(1956), 955-957.

The S-value is dependent on the silica content, the viscosity, and thedensity of the silica sol. A high S-value indicates a low microgelcontent. The S-value represents the amount of SiO₂ in percent by weightpresent in the disperse phase of the silica sol. The degree of microgelcan be controlled during the production process of silica sols asfurther described in e.g. U.S. Pat. No. 5,368,833.

According to one preferred embodiment of the invention, the S-value ishigher than about 73%, preferably higher than about 74%, even morepreferably higher than about 75%. Preferably, the S-value is lower thanabout 90%, and most preferably lower than about 85%.

The silica sol comprises silica particles suitably having an averageparticle diameter ranging from about 3 to about 150 nm, preferably fromabout 12 to about 50 nm, and most preferably from about 12 to about 40nm. Suitably, the silica particles have a specific surface area of fromabout 20 to about 900, preferably from about 40 to about 230, and mostpreferably from about 60 to about 220 m²/g. The density of the silicasol suitably is from about 1 to about 1.6, preferably from about 1.1 toabout 1.5, and most preferably from about 1.2 to about 1.4 kg/m³.

The silica sol is suitably substantially monodisperse, i.e. having asnarrow particle size distribution as possible. Suitably, the silicaparticles have a relative standard deviation of the particle sizedistribution lower than about 15% by numbers, preferably lower than 10%by numbers, and most preferably lower than about 8% by numbers. Therelative standard deviation of the particle size distribution is theratio between the mean particle size by numbers and the standarddeviation of the particle size distribution. The silica particles of thesilica sol are suitably dispersed in water in presence of stabilisingcations such as K⁺, Na⁺, Lt⁺, NH₄ ⁺ or the like or mixtures thereof.However, also other dispersions such as organic solvents, e.g. loweralcohols, acetone or mixtures thereof may be used. The pH of thedispersion suitably is from about 1 to about 12, preferably from about 7to about 11. As long as the silica sol remains stable, i.e.substantially without any aggregation or gelation, a high silica contentis preferred in the silica sol. This is beneficial in view of thesuperior technical performance of a highly concentrated silica sol andthe reduced transportation cost thereof. According to one embodiment,the ingredients, i.e. the silica sol and the gelling agent areseparately added to the applied point to be sealed. This may beperformed e.g. by means of so called jet grouting, wherein theingredients are mixed in situ, e.g. in the soil.

By the terms “silica sol” and “silica particle” are herein also meant tocomprise e.g. aluminium-modified silica particles and sols, andboron-modified silica particles and sols. Boron-modified silica sols aredescribed in e.g. U.S. Pat. No. 2,630,410. Aluminium modified silicasols, sometimes also referred to as aluminate modified silica sols, canbe prepared by adding an appropriate amount of aluminate ions, Al(OH)₄⁻, to a conventional non-modified silica sol under agitation andheating. Suitably, a diluted sodium or potassium aluminate solutioncorresponding to an aluminium modification of from about 0.05 to about2, preferably from about 0.1 to about 2 Al atoms/nm² surface area of thesilica particle is used. The aluminium-modified silica particlescomprise inserted or exchanged aluminate ions, creating aluminosilicatesites having a fixed negative surface charge. The pH of thealuminium-modified silica sol can be adjusted, preferably by means of anion exchange resin, suitably to a pH ranging from about 3 to about 11,preferably from about 4 to about 10. The aluminium modified silicaparticles suitably have an Al₂O₃ content of from about 0.05 to about 3wt %, preferably from about 0.1 to about 2 wt %. The procedure ofpreparing an aluminium modified silica sol is further described e.g. in“The Chemistry of Silica”, by ller, K. Ralph, pages 407-409, John Wiley& Sons (1979) and in U.S. Pat. No. 5,368,833.

The gelling agent suitably is an inorganic salt or acid, an organic saltsuch as sodium acetate, or acid such as acetic acid, but preferably aninorganic salt such as potassium chloride, calcium chloride, sodiumchloride, magnesium chloride, magnesium sulphate, potassium iodidemagnesium nitrate, sodium nitrate, potassium nitrate, calcium nitrate,and sodium silicate or mixtures thereof, preferably calcium chloride,sodium chloride or potassium chloride, and most preferably sodiumchloride, sodium aluminate.

A gel time regulator such as an acidic triacetine (glycerinetriacetate), diacetine, Glauber's salt (NaSO₄*10H₂O), sulphuric acid,phosphoric acid or mixtures thereof may also be added to the sealingcomposition to control the gelation thereof.

The term “gel time”, as used herein, means the amount of time elapsedfrom the moment of mixing the ingredients making up the sealingcomposition until the time when the sealing composition becomes tooviscous to move or insert to a leaking point. The viscosity is suitablycontrolled in such way that a homogeneous moving front of thecomposition is formed moving in the direction of the point to be sealed.Suitably, the initial viscosity of the sealing composition is from about3 to about 100, preferably from about 4 to about 30 mPas. The gel timemay easily be controlled by adjustment of the amount of gelling agent.Sometimes, instantaneous gelling without substantial dilution of thecomposition is necessitated to provide a gelled pressure-resistingsealing composition. A short gel time may be optimal in cracks beingrelatively ground and where the risk for rapid dilution of the sealingcomposition exists. In some cases, it is essential especially in cracksthat the gelling preferably should not start before the front of theinserted composition has fully penetrated the crack. Usually, the geltime ranges from about 1 to about 120, preferably from about 2 to about60, more preferably from about 5 to about 40, and most preferably fromabout 5 to about 20 minutes in rock sealing. In soil sealing, the geltime usually ranges from about 5 minutes to about 24 hours, preferablyfrom about 10 minutes to about 6 hours, and most preferably from about15 minutes to about 3 hours.

The ingredients may be mixed at ambient temperature. The gelling agentis suitably added to the silica sol in an aqueous solution in aconcentration from about 1 to about 30 wt %, preferably from about 2 toabout 15 wt %. The silica sol, to which the gelling agent suitably isadded, suitably has a silica content of from about 1 to about 70,preferably from about 20 to about 60, and most preferably from about 35to about 50 wt %. A high silica content in the silica sol may in manyinstances be favourable due to reduced transportation costs of silicasol.

The silica content in the sealing composition suitably is from about 1to about 60, preferably from about 15 to about 50, and most preferablyfrom about 30 to about 45 wt %. A high silica content minimisesshrinkage and maximises long term strength. The weight ratio of silicato gelling agent depends on the application and may vary depending onthe application. Suitably, the weight ratio of silica particles: gellingagent is from about 400:1 to about 10:1, preferably from about 200:1 toabout 20:1.

The gelling agent content in the sealing composition may vary dependingon the type of gelling agent used. However, the gelling agent contentsuitably is from about 0.1 to about 10, preferably from about 0.2 toabout 5 wt % of the composition. If sodium chloride is used as gellingagent, the content suitably is from about 0.2 to about 5, preferablyfrom about 1 to about 3, and most preferably from about 1.5 to about 2wt % of the composition. If calcium chloride is used as gelling agent,the content suitably is from about 0.1 to about 2, preferably from about0.2 to about 1, and most preferably from about 0.25 to about 0.5 wt % ofthe composition.

According to a preferred embodiment, the sealing composition is insertedby injecting the silica sol separately to a leaking part or cavitywhereby the sealing composition is formed in situ, e.g. in a crack of arock or a cavity in the soil. The gelling agent may thus also beseparately injected to the leaking part or cavity. This may be performede.g. by injecting the sealing ingredients simultaneously, e.g. byplacing injection nozzles for the silica sol and the gelling agent inparallel such that the gelling agent and the silica sol can be injectedat the same time without premixing. However, in certain leaking parts orcavities, e.g. in soil, a gelling agent in the form of e.g. a salt mayalready be present in the soil in such quantity that no further gellingagent need to be added to form a sealing composition. Hence, in onepreferred embodiment of the invention, solely silica sol is separatelyinjected to a leaking part or cavity. The method can generally impartcutting off of any liquid flow of e.g. water and aqueous solutions,organic solutions etc, but the method is principally adapted to cut offflow of water and aqueous solutions.

The sealing composition may also be inserted to a leaking part or cavityby means of other methods such as jet grouting, in which at least a partof the material constituting the leaking part or cavity is removed toadd the sealing composition and then reset to the same point from whichit was earlier removed with the sealing composition incorporatedtherein. This method is preferably adapted to be used in the sealing ofsoil.

According to one preferred embodiment, the silica sol and the gellingagent are mixed immediately before injection. In this context, thewording “immediate” means from about 0 to about 30 seconds, preferablyfrom about 0 to about 15 seconds. This way of mixing the ingredients ofa composition is often referred to as in-line mixing.

According to one preferred embodiment, the sealing composition may alsobe prepared in a batch process in advance and used suitably within 60minutes, and preferably within 30 minutes before insertion of thecomposition. This way of preparing the sealing composition, however,necessitates a sufficiently stable sealing composition that can bestored without substantial gelling until the moment of insertion. Theinjection time of the sealing composition is suitably from about 1minute to about 1 hour, preferably from about 5 minutes to about 30minutes. The injection/penetration depth varies of course with the leakto be sealed. However, the method of the present invention isparticularly beneficial for depths from about 0.5 to about 50 meters,preferably from about 5 to about 30 meters. The injection pressuresuitably is from about 1 to about 50 bar, preferably from about 2 toabout 25 bar.

The sealing composition is principally adapted to provide barriers inthe subsurface for preventing leakage of water. The sealing of rockinvolves insertion of the sealing composition into e.g. a cavity such asa microcrack, especially to control groundwater leakage, e.g. intunnels. By the term “microcrack” is usually meant a cavity having adiameter lower than 20 μm. As the diameter of the silica particles inthe silica sol is from about 10 to about 100 nm, sealing compositionscontaining such silica particles are of course suitable for injectioninto microcracks.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the gist and scope of the present invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the claims. The following exampleswill further illustrate how the described invention may be performedwithout limiting the scope of it.

EXAMPLE 1

Sealing compositions were prepared from a salt solution of 1.7 M sodiumchloride which was added under agitation to 200 g of different silicasol products as defined in the tables below. The amount of salt solutionadded was 40 g solution in all compositions. The compositions were agedup to 672 hours to evaluate the long term shear strength. In table 1,one set of the compositions was exposed to an increased temperature of55 DC and another set was exposed to a pH of 12 to accelerate the ageingof the sealing composition. The calculation of the particle diameter ofthe silica particles was made by Sear's method for calculating thespecific surface area. The shear strength test was performed with thefall cone test according to the Swedish Standard SS 02 71 25.

Also the compressive strength was determined for the sealingcompositions. This was made by compression tests in which a load-frame,a pressure-head with the same diameter as the sample, a load cell with aplane surface where the sample is placed between the load-cell and thepressure-head, a displacement transducer, a battery powered data-logger,a signal processing software were used. The load frame forces thepressure-head to move in vertical direction. The frame is of same typeas used in machine shops for controlled vertical drilling. The load iscontrolled by weights, which loads the load-head without anytransmission (dead weight). The pressure-head consists of a rigid steelcylinder with 50 mm diameter. The load-cell has a capacity for 300 kg.The load-cell forms a plane surface. The sample is situated between theload-cell and the pressure-head. The accuracy for the load-cell iswithin 0.1 kg. The displacement transducer has a stroke capacity of 5mm. The error of the actual transducer was tested by the factory to max0.4%. The data-logger used for the tests is developed to monitorvibrations and deformations during field conditions. The logger monitorscontinuously during the test. The compression tests were performed onlyfor samples cured during 28 days. The mould-cylinders size was 50 mmdiameter and 25 mm height. The mould cylinders were positioned in a potwith a plane bottom. The sealing composition was then poured up to theupper end of the cylinders. All samples were cured in 20° C. water bathat pH 10. Only the cross sections where exposed to water. Beforetesting, the samples were separated from the mould-cylinders.

TABLE 1 Compo- Surface Shear Shear sitions made area strength strengthwith the Particle on product (kPa), (kPa), following diameter S- base55° C., 20° C., pH sols: (nm) value (m²/g) pH 10, 672 h 12, 672 h Sol 117 77 68 326 — Sol 2 12 76 88 640 475 Sol 3 11 70 100 218 — Sol 4 7 70108 250  70 Sol 5 5 45 7 48  39

In table 1, it can be seen that the sealing compositions made fromsilica sols having an S-value according to the invention results in ahigher gel strength after 672 hours than the composition prepared fromthe comparative silica sols 3-5, both at ambient temperature and at a pHof 12 (which accelerates the ageing of the products) and at a pH of 10and a temperature of 55° C. (which also results in a faster ageingprocess).

TABLE 2 Compositions Surface Compressive made from Particle area onstrength the following diameter S- product (kPa)/max sols: (nm) valuebase (m²/g) load Sol 6 35 90 40 48 Sol 1 17 77 68 50 Sol 2 12 76 88 45Sol 3 11 70 100 11 Sol S 5 45 75 11

In table 2, it can be seen that the sealing compositions prepared fromthe silica sols with an S-value in accordance with the present inventionimpart higher compressive strength than the sealing compositions madefrom the comparative silica sols 3 and 5.

1. A method for sealing rock or soil comprising inserting a sealingcomposition obtained by mixing a silica sol and at least one gellingagent into said rock or soil, wherein the silica sol has a S-valuehigher than about 72% and a silica content in the range from about 20 toabout 70 wt %.
 2. A method according to claim 1, wherein the S-value ishigher than about 75%.
 3. A method according to claim 1, wherein thesilica sol is an aluminium modified silica sol.
 4. A sealing compositionaccording to claim 3, wherein the composition has a weight ratio ofsilica particles to gelling agent from about 400:1 to about 10:1.
 5. Amethod according to claim 1, wherein the composition has a silicacontent from about 35 to about 50 wt %.
 6. A method according to claim1, wherein the gelling agent is selected from the group consisting ofpotassium chloride, sodium chloride, calcium chloride, magnesiumchloride, magnesium nitrate, magnesium sulfate and mixtures thereof. 7.A method according to claim 1, wherein the composition has a relativestandard deviation of the particle size distribution lower than about15% by numbers.
 8. A method according to claim 1, wherein thecomposition has a gelling agent content from about 0.2 to about 5 wt %.9. A method according to claim 1, wherein the silica sol comprisessilica particles having a specific surface area from about 40 to about230 m²/g.
 10. A method according to claim 1, wherein the composition hasa weight ratio of silica particles to gelling agent from about 400:1 toabout 10:1.
 11. A method according to claim 1, wherein the compositioncontains silica particles having a size within the range of from aboutto about 12-50 nm.
 12. A method according to claim 1 for sealing rock.13. A method of sealing a leaking crack or cavity in rock or soilcomprising inserting into the crack or cavity at least one gellingagent; and separately inserting into the crack or cavity a silica solhaving an S-value higher than about 72% and a silica content in therange from about 20 to about 70 wt %; wherein the gelling agent and thesilica sol mix in situ to form a seal in the crack or cavity.
 14. Amethod of sealing a leaking crack or cavity in soil comprising insertinginto the crack or cavity a silica sol having an S-value higher thanabout 72% and a silica content in the range from about 20 to about 70 wt%, wherein at least one gelling agent is present in the soil in agelling effective amount and the gelling agent mixes with the silica solto form a seal in the crack or cavity.
 15. A method for sealing rock orsoil comprising inserting a sealing composition at an injection pressurefrom about 2 to about 25 bar obtained by mixing a silica sol and atleast one gelling agent into the rock or soil, wherein the silica solhas a S-value higher than about 72% and a silica content in the rangefrom about 20 wt % to about 70 wt %.